Radical polymerization constitutes one of the polymerization processes which is most frequently exploited industrially on account of the variety of polymerizable monomers, the ease of implementation and the ease of the synthetic processes employed (bulk, emulsion, solution or suspension polymerization). However, it is difficult in standard radical polymerization to control the polymer chain size and the molecular mass distribution. Materials consisting of these macromolecules thus do not have controlled physiochemical properties. Furthermore, standard radical polymerization does not lead to block copolymers.
Ionic or coordinative polymerizations make it possible themselves to control the process of addition of the monomer, but they require careful polymerization conditions, in particular a high level of purity of the monomer and of the reactants, as well as an inert atmosphere.
The aim is to be able to carry out radical polymerizations which afford better control over the various parameters mentioned above and which can lead to block copolymers.
The concept used for controlling the polymerization involves redox reactions for transferring atoms or groups of atoms reversibly. The metal complex oscillates permanently between two oxidation states during the polymerization. This concept has been widely exploited in organic chemistry and was discovered by Kharasch in 1947 with the addition of polyhalomethanes to olefins.
The following systems have been used successfully to control the polymerization:
RuCl.sub.2 (PPh.sub.3).sub.3 in the presence of an aluminium derivative: this type of system, which involves an aluminium derivative, is sensitive to oxygen and to moisture. PA0 CuCl/bipyridine: copper systems work at high temperatures, for example above 100.degree. C. for styrene. PA0 Van Koten complexes, which are organometallic complexes of nickel (thus possessing a metal-carbon bond); they have the drawback of having a long preparation which involves several synthetic steps, in particular that of the starting ligand; furthermore, they are oxygen-sensitive and must therefore be employed under anaerobic conditions. PA0 nickel reduced to oxidation state (0) has been used in the presence of alkyl halides (Otsu, T. Chem. Express 1990, 5, 801 or Otsu, T. J. Macromol. Sci. Chem. 1969, 3, 177) in order to carry out a live polymerization of methyl methacrylate, but bimodal distributions are obtained. Similarly, activated nickel metal may serve as an initiator in the presence of alkyl halide (Otsu, T. J. Polym. Sci., Polym. Lett. 1967, 5, 697 or Otsu, T. J. Polym. Sci. Part A1, 1970, 8, 785) in order to polymerize methyl methacrylate, but no live nature is mentioned. PA0 at least one radical-generator compound other than an arenesulphonyl chloride; and PA0 at least one catalyst consisting essentially of a metal complex represented by formula (I) below: EQU MA.sub.a (L).sub.n (I) PA0 M represents Ni, Pd or Pt; PA0 A represents a halogen or a pseudohalide; PA0 the groups L are ligands of the metal M, which are chosen independently from those containing at least one from among N, P, As, Sb, and Bi, it being possible for at least two of these ligands to be connected together by one or more divalent radicals; PA0 a is an integer from 1 to 5; PA0 n is an integer from 1 to 4; PA0 Y.sup.1 represents: PA0 diphosphines such as, for example: PA0 arsines such as: PA0 R.sub.1 to R.sub.4 each chosen from alkyl and aryl; and PA0 n=1 to 10, PA0 or R.sub.1 represents: ##STR30## R.sub.2 and R'.sub.2 then being identical and representing a group chosen from hydrogen, C.sub.1 -C.sub.4 lower alkyl, C.sub.1 -C.sub.4 alkoxy and halogen. PA0 (a) derivatives of formula: EQU CYZ.sub.3 PA0 (b) derivatives of formula: EQU R.sup.3 CCl.sub.3 PA0 (c) derivatives of formula: ##STR32## in which: Q represents a chlorine or bromine atom or an acetate ##STR33## or trifluoroacetate ##STR34## or triflate (O.sub.3 SCF.sub.3) group; RS represents a hydrogen atom, a C.sub.1 -C.sub.14 alkyl group or an aromatic group of the benzene, anthracene or naphthalene type, for example, or a --CH.sub.2 OH group; PA0 (d) .alpha.-halo lactone or lactam compounds such as .alpha.-bromo-.alpha.-methyl-.gamma.-butyrolactone or .alpha.-bromo-.gamma.-valerolactone, halogenated lauryllactam or halogenated caprolactam; PA0 (e) N-halosuccinimides, such as N-bromosuccinimide, and N-halophthalimides, such as N-bromophthalimide; PA0 (f) alkylsulphonyl halides (chlorides and bromides), the alkyl residue being C.sub.1 -C.sub.14 in particular; PA0 (g) compounds of the formula: ##STR37## where: R.sup.10 represents a hydrogen atom, a C.sub.1 -C.sub.14 alkyl group or a carboxylic acid, ester, nitrile or ketone group; PA0 (h) compounds of formula: ##STR38## where: R.sup.12 represents C.sub.1 -C.sub.14 alkyl or aryl; and PA0 (i) compounds of formula: ##STR39## where: R.sup.13, R.sup.14 and R.sup.15 each independently represent C.sub.1 -C.sub.14 alkyl or aryl; and PA0 (j) aromatic halides of formula: EQU Ar--U PA0 A.sup.1 --(CH.sub.2).sub.p --A.sup.2 with p being an integer from 1 to 14, and ##STR40## with q and r each independently representing an integer from 1 to 14. PA0 Q' and Q" each independently represent a group falling within the definition of Q PA0 R.sup.6' and R.sup.6" each independently represent a group falling within the definition of R.sup.6 ; and PA0 R.sup.16 represents a group --(CH.sub.2).sub.p --, ##STR42## as defined above. PA0 aromatic hydrocarbons (apolar aprotic): benzene, toluene, ethylbenzene, xylene; PA0 chlorinated hydrocarbons (polar aprotic): methylene chloride, chlorobenzene; PA0 ethers such as diphenyl ether PA0 cyclic ethers (polar aprotic): tetrahydrofuran, dioxane; PA0 esters (polar): ethyl acetate, cyclohexyl acetate; PA0 ketones (polar): methyl ethyl ketone, cyclohexanone. PA0 homogeneous and live polymerization. The polymerization is live according to the criteria generally put forward: linear change in the average masses as a function of the conversion, linear change in ln(1/(1 PA0 excellent molecular control: Mw/Mn narrow up to about Mw/Mn=1.1; good correlation between the theoretical Mn and the experimental Mn; possibility of preparing block copolymers, including star-shaped copolymers; PA0 quantitative polymerization leading to total consumption of the monomer; PA0 mild temperature conditions ranging from 0.degree. C. to 130.degree. C. and ordinary pressure; PA0 the reaction time depends on the concentration of the reaction medium. This is because, the lower the concentration of monomer, the slower will be the polymerization kinetics. In concentrated medium ([monomer]&gt;6 mol 1.sup.-1), the polymerization may be terminated in less than two hours. In more dilute medium, the polymerizations are generally stopped after reacting for 24 hours; PA0 compatibility in aqueous media since the catalysts used do not degrade in the presence of water. Possibility of emulsion and suspension polymerization, in the presence or absence of emulsifiers, the use of soluble phosphines such as, for example, (Na.sup.+ O.sub.3 SC.sub.6 H.sub.4).sub.3 P) making it possible to dissolve the complex in the aqueous phase; PA0 possibility of stereocontrol, that is to say of controlling the hetero-, syndio- or isotacticity by using chiral catalysts; PA0 excellent control of the synthesis of the polymers or copolymers obtained, the molecular masses of which range between 400 and 10,000,000 g/mol; PA0 the resistance to thermal degradation of the polymers and copolymers is improved on account of the absence of termination reactions (combinations and disproportionations) which may be shown in particular by thermogravimetric analysis; PA0 production of novel products that are difficult to access by the usual polymerization techniques, such as pure block copolymers, defined random copolymers and hyperbranched polymers which can be used as adhesives of controlled formulation, shockproof additives, emulsifiers and interface agents; PA0 production of materials with improved properties; the absence of terminal double bonds makes it possible to increase the depolymerization temperature of the polymers, in particular of PMMA; PA0 controlled polymerization which makes it possible to avoid the auto-acceleration of the polymerization (known as the gel effect or Trommsdorf effect). The control of the polymerization by the nickel complex makes it possible to avoid the sudden auto-acceleration of the polymerization after very rapid setting (see Comparative Example 6). This phenomenon is generally harmful for the manufacturer and the product. In particular, for PMMA which needs to be in the form of cast plates, it is important for the polymerization to be controlled in order to avoid the appearance of bubbles or defects at the surface of the plate. The gel point may be avoided by using suitable, sometimes long, temperature cycles. A single temperature is preferably used, which is a simplification for the process.
With bipyridine as ligand, the complex is insoluble in the monomer. In order to achieve dissolution, it is necessary to use substituted bipyridines, such as dinonylbipyridine.
At the present time, few articles make reference to nickel complexes in order to control the radical polymerization. However, mention may be made of:
Other complexes of nickel in oxidation state (0), such as Ni{P(OR).sub.3 }.sub.4 (Hargreaves, K. J. Polym. Sci. Polym. Chem. 1988, 26, 465) or Ni[CO].sub.4 (Bamford, C. H. Trans. Farad. Soc. 1970, 66, 2598) have been tested in the presence of alkyl halides as initiators of vinyl monomers, but no mention is made of live nature.
Complexes of the type NiX.sub.2 (PPh.sub.3).sub.2 have been used to carry out the Kharasch addition (Inoue, Y. Chem. Lett. 1978, 367) but not to carry out the controlled radical polymerization. Percec et al. in Macromolecules 1996, 29, 3665-3668 cite these complexes for carrying out the Kharasch addition, and mention that with arenesulphonyl chlorides, the polymerization of styrene is not controlled. No mention is made of good control (and thus live nature) of the polymerization with this complex and a radical generator, in particular an alkyl halide such as CBrCl.sub.3.